While statistics from hospitals showed that the proportion of self-harm or attempted suicide kept growing among children and adolescents aged 6–17 attending the emergency department, cases of self-harm or attempted suicide dissimulated as accidents received scant attention or were neglected. This study aimed to examine associations between unintentional injuries subtypes and deliberate self-harm behaviors from a school-based large-scale survey. A school-based cross-sectional study was conducted in Anhui, China, between November 2022 to January 2023. A total of 28,013 students (aged 11–17, 5th–12th grade) from 35 primary schools, 27 middle schools, and 6 high schools were included for the present study. Unintentional injuries in the past year of children and adolescents reported by parents. Self-harm behaviors in the past year of children and adolescents was measured with one question reported by students. Children and adolescents whose parents reported their contacts with sharp instruments demonstrated the highest risk for self-harm behaviors, followed by poisoning, exposure to electric current, falls, vehicle and traffic injuries, accidental drowning and submersion, and eating foreign bodies. And these associations distributed differently among children and adolescents reporting different frequencies of self-harm behaviors. Thus, we urge attention from parents, child caregivers, and teachers on children and adolescents experiencing certain types of unintentional injuries.